MSN Messenger users using non @firstname.lastname@example.org email address's for their MSN Messenger logins maybe experiencing problems with the service this evening. The common error message is :
We could not sign you in to MSN Messenger because there is a problem with your .NET Passport. Click OK to learn more at the .NET Passport Web site. 81000303. Clicking ok results in another error message, Microsoft® .NET Passport was temporarily unable to complete your request. Please try again later. Although the messenger status page hasn't been updated to reflect this problem we've spoken to sources close to MSN Support who have confirmed outage for many customers.
Update: Microsoft have confirmed this is a problem with the .NET Passport Service rather than the MSN Messenger Service, engineers are currently working on a solution.
Update 2: It appears the MSN Passport team have now fixed the problem, happy IMing!